The presence of Her-2, estrogen receptor (ER) or progesterone receptor (P) on breast cancer cells is a very important biomarker which facilitates physicians in making decisions on treatment schemes and in proposing prognosis of the disease. Current methods for diagnostic and prognostic classifications of ER, PR and Her2/neu are based on immunohistochemistry (IHC), a technique that has been used in clinical medicine for over 80 years. However, the immunoenzyme (HRP-based) IHC method has a single color nature and is unable to perform multiplexed molecular profiling. Moreover, IHC remains semi-quantitative and subjective, resulting in considerable inter-observer variations of results. Semiconductor nanocrystals also known as quantum dots (QDs) are a new class of biological detection labels, which present a broad range of biomedical applications including multicolor labeling, single molecule biophysics, biomolecular profiling, optical barcoding, and in vitro and in vivo imaging. Current studies have indicated that QDs can be used for multiplex detection of ER, PR and Her2 in breast tumor tissue. In Phase I work, we have demonstrated that genetic engineered protein G fragment can serve as universal linker to conjugate nanoparticles with antibodies, which presented the probes with small size and antibody orientation. In phase II, we will first separate the circulating cancer cells and then quantitatively analyze the expression levels of ER, PR and Her2/neu biomarkers in a multiplexed fashion. Our overall goal is to develop an assay that is capable of isolating circulating cancer cells while quantifing the expression levels of a panel of cancer biomarkers to provide guidance for cancer treatment. 1 PUBLIC HEALTH RELEVANCE: Breast cancer is the second leading cause of death in the United States. In 2007, about 1,444,920 new cancer cases were expected to be diagnosed, and about 559,650 Americans were expected to die of cancer-more than 1,500 people per day. The presence of several important biomarkers on breast cancer cells is a very important diagnostic criterion, which facilitates physicians in making decisions on treatment schemes and in proposing prognosis of the disease. However it has been difficult to accurately, simultaneously measure the expression levels of these receptors. The development of nanotechnology, especially the development of bioconjugated nanoparticles provides an essential solution. Successful development of this project will significantly advance the technique of multiplex quantification of expression levels of various cancer receptors and provide valuable guidance for more effective treatments.